Lightweight composite camshaft

ABSTRACT

A lightweight composite camshaft has stamped sheet metal or other lightweight journal and/or cam elements having locating hubs and assembled onto a hollow tube. An economical and rapid method of assembly uses indexing balls pressed into accurately positioned blind holes in the tube and grooves in the bores or hubs of the cam elements to angularly locate the cams with precision prior to locking them tightly in place by expansion of the tube.

TECHNICAL FIELD

This invention relates to camshafts for internal combustion engines andthe like. In particular the invention relates to assembled or compositecamshafts and methods for their manufacture.

BACKGROUND

U. S. Pat. Nos. 4,567,365 issued Jul. 1, 1986 and 4,835,832 issued Jun.6 1989 to the assignee of the present invention and German patentapplication publication DE 3346056 A1 published Jul. 19, 1984 disclosevarious forms of assembled or composite camshafts and methods for theirassembly. The U.S. patents involve composite camshafts assembled fromindividual elements such as cams and journals mounted on a hollow tubeby mechanical expansion with a ball or mandrel. The German publicationshows a hollow camshaft made up of separate hollow elements connected byfriction welding. One embodiment includes lightweight formed sheet metaljournals.

U. S. Pat. No. 4,638,683 issued Jan. 27, 1987 discloses compositecamshafts having ceramic cam sections connected by interference fittedmetallic sleeves. Balls received in shaft dimples and engaging groovesin the sleeves are provided for locating and locking the elements intheir desired angular orientations.

SUMMARY OF THE INVENTION

The present invention provides modified camshaft structures and assemblymethods wherein lightweight camshaft assemblies may be made usingpreviously known tube expansion methods as well as modifications of suchmethods. The composite lightweight camshafts preferably have lightweighthollow core journal and/or cam elements including hubs suitable forassembly of the elements on a tube by mechanical expansion. The hubportion of each element has adequate length to guide and support theelement on the tube and adequate strength to avoid distortion duringtube expansion.

Assembly methods depart from known processes in using a timing procedurewherein balls are embedded in undersized premachined dimples comprisingshallow blind holes or recesses in a tube and positioning pregroovedelements on the tube to provide accurate timing of the elements prior totube expansion for locking the components together.

These and other features and advantages of the invention will be morefully understood from the following description of certain specificembodiments of the invention taken together with the accompanyingdrawings.

BRIEF DRAWING DESCRIPTION

In the drawings:

FIG. 1 is a fragmentary pictorial view of an engine camshaft havinglightweight formed bearing journals according to the invention;

FIG. 2 is a fragmentary pictorial view of an engine camshaft havinglightweight formed cam elements according to the invention;

FIGS. 3 and 4 are end and transverse cross-sectional views of anexemplary alternative embodiment of lightweight bearing journal;

FIGS. 5 and 6 are end and transverse cross-sectional views of anotheralternative embodiment of lightweight bearing journal;

FIGS. 7 and 8 are end and transverse cross-sectional views of stillanother alternative embodiment of lightweight cam element;

FIG. 9 is a pictorial view illustrating a step in a modified method ofcomposite camshaft assembly according to the invention;

FIG. 10 is a pictorial view showing a later step in the assembly method;and

FIG. 11 is a cross-sectional view through a cam of a finished camshaftassembled by the method of FIGS. 9 and 10.

DETAILED DESCRIPTION

Referring now to the drawings in detail, FIG. 1 shows a portion of acomposite or assembled camshaft 10 which is generally of the type shownin our earlier U.S. Pat. No. 4,835,832, noted above. Camshaft 10includes a hollow supporting shaft or tube 11 on which are mounted anumber of cam elements 12 and journal elements 14 using any suitablemanner of assembly including methods of mechanical tube expansion asdisclosed, for example, in U.S. Pat. No. 4,835,832 and subsequentlyherein.

The FIG. 1 embodiment differs from the prior disclosures in theprovision of a lightweight bearing journal 14 in place of the solidjournal shown in the earlier patent. The journal 14 includes acylindrical outer wall 15 connected at one end by a solid web or endwall 16 with a hub 18 that extends parallel with the outer wall andfixes the journal squarely and solidly in place on the tube 11. Theshape leaves within the journal a hollow annulus 19 open at one endwhich reduces the mass of the journal element as compared to solidelements.

The journal 14 is preferably made by stamping or roll forming from asheet metal blank, although any other suitable method of making could beused. Mass metal forming such as hot or cold forming from bar stock andpowder metal forming are examples. The strength of the walls and, thus,their thicknesses must be adequate for their functions, the outer wall15 to engage the bearing, the end wall 16 to support the outer wall andthe hub 18 to withstand the forces resulting from assembly of thejournal 14 on the tube 11 as well as the loads placed on the journal.

FIG. 2 shows a portion of a composite or assembled camshaft 20 which issimilar to camshaft 10 but also includes lightweight cams 22 which maybe formed similarly to the journals 14. The cams also include hubs 23,end walls 24 and outer walls 26 for similar purposes as in the journalsand subject to similar strength and thickness requirements to accomplishtheir functions. Obviously, the outer walls in use engage cam followersfor actuating engine valve gear in known manner.

FIGS. 3-8 show other embodiments of lightweight journal and cam elementswhich could be used in composite camshafts. In FIGS. 3 and 4, bearingjournal 27 has alternately oppositely opening recesses 28 that leave astaggered web 30 connecting the hub 31 with the outer wall 32. In FIGS.5 and 6, journal 33 has lightening holes 34 extending axially through anotherwise solid body to form radial spokes 35 connecting a hub 36 withan outer wall 37. FIGS. 7 and 8 show a cam element 38 with side recesses39 in the nose for lightening. This embodiment is applicable to smallercams where formed sheet metal could not be utilized. All the embodimentsof FIGS. 3-8 are suitable for mass metal forming.

The camshafts so far described can be suitably manufactured using themethods, equipment and construction features disclosed in the noted U.S.Pat. No. 4,835,832. However, FIGS. 9-11 illustrate a variation of thismethod which avoids the need for specific assembly fixtures andsignificantly reduces the cost of manufacturing new design or low volumecamshaft assemblies.

In this method, a camshaft assembly 40 is prepared for the tubeexpansion step of U.S. Pat. No. 4,835,832 by locating cam elements orcams 41 on the tube 42 with small locating or timing balls 43 which maybe hardened steel bearing balls. The balls engage slightly undersizegrooves 44 in the bores 46 in the bodies or hubs of the cam elements 41and slightly undersize blind holes 47 in the outside 48 of the tube 42to accurately fix by interference fit the cam elements in their properangular orientations for the tube expansion step. This results inaccurate timing of the cams in the resulting assembled compositecamshaft.

The modified assembly method of this invention begins with the mountingof the tube or shaft 42 in the rotatable head or chuck 50 of an indexingmachine such as a four axis computer numerically controlled (CNC) mill,with a drill head 51 as shown in FIG. 9. The tube is sequentiallyrotationally indexed and the drill head or the tube is advancedlongitudinally to the proper positions at which cams are to be locatedand a blind index hole 47 is drilled at a precisely controlled point ateach location.

Also, prior to assembly, the individual cam elements 41 and journalelements 54 to be assembled on the tube 42 are formed in any suitablemanner along with any gears, flanges or other components (not shown) tobe included in the assembly. The cams and journals may be lightweightelements as in the embodiments of FIGS. 1-8 or they may be solid asshown in prior U.S. Pat. No. 4,835,832. They may be hardened as desiredand are preferably ground or otherwise formed to their proper widthsprior to assembly.

The cams 41 are each provided with a bore 46 sized for close fittingover the outer diameter 48 of the tube 42. Preferably the bore 46 isformed with a special shape as disclosed in the prior U.S. Pat. No.4,835,832. The bore is also provided with a shallow groove 44 forreceiving a timing ball 43. A steel bearing ball with a diameter of 1/8inch (3.175 mm) has been found suitable for use as a timing ball in anautomotive engine camshaft as described in the prior patent. Each groovemust be formed in a known angular location relative to the cam form, andmay, for convenience, be centered on the longest diameter 55 passingthrough the high point or tip of the nose 56 of the raised lobe of itsrespective cam. Extreme accuracy may be obtained, for example, byforming the periphery of the lobe and locating the timing groove in thesame machining operation. The blind holes 47 and the cam grooves 44 arepreferably sized with diameters (or radii) slightly smaller (e.g. 0.002in or 0.051 mm) than the ball 43.

After this preparation, the cams, journals and other elements areassembled in sequence on the tube 42 as shown in FIG. 10. The tube 42 ispreferably positioned vertically for this step, although it may beotherwise positioned, e.g. horizontally, if desired. As the elements arelocated sequentially on the tube, C-shaped spacers 58, each having aslot 59, are slid over the tube between each adjacent pair of elements41, 54 to properly control the longitudinal spacing and positions of theelements. This is similar to the assembly process described in U.S. Pat.No. 4,835,832. The spacers are preferably positioned with their slots 59opening in the same direction for convenience in the subsequent tubeexpansion step.

Prior to assembly of each cam element 41, a ball 43 is placed into theblind indexing hole 47 for that cam and is held in place while the camelement 41 is slid onto the tube 42 with its groove 44 engaging the ball43. The element 41 is then forced over the ball 43 until it engages thespacer 58 which locates the element longitudinally on the tube 42.Because the diameters of the blind hole 47 and groove 44 are slightlysmaller than the ball 43, the ball engages the edges of both the hole 47and groove 44 and deforms them slightly upon assembly. This closelypositions the groove 44 in alignment with the hole 47 to accuratelyindex the cam element 41 angularly on the tube 42. Ball location is notused with the journals 54 or other elements which are symmetrical and donot require angular positioning.

When all the elements 41, 54 etc. have been assembled sequentially onthe tube with the cams angularly positioned in the manner just describedand C-shaped spacers 58 located between the elements for longitudinalpositioning, the assembly 40 is transferred to a simple fixture (notshown) for the tube expansion step. This fixture may be positioned withthe camshaft assembly horizontal and the slots 59 of the spacers 58facing downward for gravity retention on the tube.

Tube expansion is preferably accomplished in essentially the mannerdescribed in said U.S. Pat. No. 4,835,832, although other methods oftube expansion may be utilized. However, the fixture described in thepatent may be simplified since it does not need to locate the cams (asthis is done by the locating balls 43) and needs only to restrain thecamshaft from bending, such as by restraining the journal elements 54against lateral motion. This simplification avoids the need forexpensive fixtures to be provided for each new camshaft assembly andgreatly increases the speed, accuracy and economy with which a new ormodified camshaft design may be assembled for testing and development.The method may also be used for production assembly but would be mostsuitable for smaller volumes where the provision of more complicatedfixtures is not economical.

After the elements 41, 54 are firmly fixed to the tube 42 by expansion,the spacers 58 are removed and the assembled composite camshaft may befinished by final machining of the cams, journals and other elements asrequired in accordance with ordinary camshaft machining procedures. Theadvantages of minimum machining requirements for assembled camshafts asin U.S. Pat. No. 4,835,832 are fully possessed by camshafts formedaccording to the present method. The advantages may be greater if theaccuracy of location of the cam elements made possible by precisionlocation of the index balls 43 is fully realized.

While the invention has been described by reference to certain preferredembodiments and methods, it should be understood that numerous changescould be made within the spirit and scope of the inventive conceptsdescribed. Accordingly it is intended that the invention not be limitedto the specifically disclosed methods and embodiments, but that it havethe full scope permitted by the language of the following claims.

What is claimed is:
 1. A lightweight composite camshaft having aplurality of separately formed cam and journal elements fixed on anouter surface of a hollow tube wherein at least some of the journalelements comprise lightweight journals havingan annular outer wall witha continuous periphery for rotatably engaging a bearing surface, anannular hub spaced inward of the outer wall and engaging the tube forsupporting said one element in predetermined relation with the tube, anda web extending radially between adjacent ends of the hub and outer walland connecting the hub and outer wall, the lightweight journals havingan open ended annular space extending axially from the web to distalends of the hub and outer wall.
 2. A lightweight composite camshaft asin claim 1 wherein at least some of the cam elements are lightened byrecesses formed in support means between a hub and outer wall.
 3. Alightweight composite camshaft as in claim 1 wherein at least some ofthe cam and journal elements are also formed of sheet metal having ahub, outer wall and interconnecting web between adjacent ends of the weband outer wall.